1. Field of the Invention
The present invention relates to lapping, polishing, finishing or smoothing of surfaces with apparatus and processes which use abrasive sheeting. The invention particularly relates to lapping apparatus and processes which can lap two faces of a work piece simultaneously. Optionally with the lapping of two surfaces on a single work piece at one time, the present invention relates to such processes and apparatus which use removable or replaceable abrasive sheeting which operates at high surface speeds, secures said abrasive sheeting to a support in an annular distribution of abrasive material on a face of the abrading platen, and which may optionaly move the sheeting at those high speeds without the use of adhesive layers between the sheeting and the support, and/or which provides a high degree of control over the contact point or contact plane of the abrasive sheeting and the article which is to be lapped, polished, finished or smoothed.
2. Background of the Art
The field of lapping or polishing traces it roots far back into time, even before substantial technical developments. Early jewelry and decorations were provided by minerals or materials (shells or wood) which had been smoothed by natural elements. Stones smoothed by water currents or sand storms gave a much more pleasant look and feel than unpolished stones or stones which had been roughly smoothed by available means such as rubbing two stones together.
Early efforts at sharpening blades for plows or swords were amongst the first technical advances in lapping and smoothing of materials, and these technical means are still used in much the same way today. Swords and plow shears were sharpened by moving the blade against a stone surface. The abrasive action of the stone against the blade removes metal and thins the blade at its edge. Grinding wheels, kitchen knife sharpeners, and the like are not significantly different in function than the stone sharpening tools, such as the grinding wheel which has been used to sharpen blades for thousands of years.
In the 17.sup.th and 18.sup.th century the combination of die casting and abrasive polishing enabled the manufacture of interchangeable generic parts for equipment (especially the rifle and hand gun) as opposed to the standard method of fitting individually made parts into a unique piece of equipment with uniquely fitting parts. Each succeeding advance in the ability of materials and processes to create smoother and more uniform surfaces advanced the quality and capability of the resultant articles to perform whatever tasks for which they were designed. Lenses with greater smoothness and uniformity advanced the degree to which observation could be extended downward into microscopy and outward into space. Better fitting parts extended the longevity of equipment and increased efficiency by reducing internal friction. The need for increasing efficiency, precision, consistency and smoothness in lapping is as important today as ever, and each incremental increase in the quality of lapping materials and processes advances many fields of technology and industry, while at the same time offering the possibility of reducing the cost of manufacture of goods.
Lapping and polishing are performed in many fields and industries. Metal and parts polishing is the most obvious field, but smoothing of surfaces is extensively used in lens manufacture, semiconductive wafer manufacture, gem polishing, preparation of supports for optical elements, and the like. The smoothness and reproducibility of the processes and apparatus used to create the needed levels of smoothness are critical to the success of products. U.S. Pat. No. 5,584,746 (Tanaka) describes a method of polishing semiconductor wafers and apparatus therefor. The import of Tanaka is the physical control placed over the wafer as it is being polished. The wafer is secured by a vacuum system on a wafer mounting plate. The relative flexibility of the wafer is discussed as a method of controlling uniformity of the wafer surface as is the uniformity of the vacuum applied through the wafer support. The polishing of the wafer surface is accomplished by typical means including a polishing pad which is mounted on a polishing surface (turntable). It is suggested that the pad should not be subject to plastic deformation and may be preferably selected from a group comprising close cell foam (e.g., polyurethane), polyurethane impregnated polyester non-woven fabric and the like, which are known materials in the art. No specific means of securing the polishing pad to the support surface is described in Tanaka. No specific speeds of rotation for the operation of the process are shown in the examples.
U.S. Pat. No. 5,317,836 (Hasegawa) describes an apparatus for polishing chamfers of a wafer. Hasegawa describes that in the manufacture of wafer materials from single crystal ingots such as silicon, the wafer is produced by a combination or selection of processes including slicing, chamfering, lapping, etching, buffing, annealing and polishing. It is noted that chipping and/or incomplete surface polishing are a problem in such ingot conversion to wafers. Hasegawa describes the use of a rotary cylindrical buff formed with at least one annular groove in its side describing a circle normal to the axis of the cylindrical buff and a wafer holder capable of holding and turning the wafer about an axis. The improvement is described as including at least the ability of the cylindrical buff being adapted to freely shift axially, that the annular groove has a width substantially greater than the thickness of the wafer, and that the apparatus further comprises a means for axially biasing the cylindrical buff. No specific speeds of rotation for the operation of the process are shown in the examples.
U.S. Pat. No. 5,007,209 (Saito) describes an optical fiber connector polishing apparatus and method. Saito describes a method and apparatus for polishing optical fiber connectors with high accuracy. Saito indicates that the polishing is accomplished by using an elastic polishing board rotating at high speed, but no specific speed of rotation or method of attachment of the polishing board is described. Positioning pins and other controls are provided in the system to accurately align the swing fulcrum arm carrying the polishing material.
U.S. Pat. No. 4,085,549 (Hodges) describes a lens polishing machine comprising a lap tool holder and lens blank holder including independent means to provide linear and rotary movement between a lens blank and lap tool. The machine is described as useful for high speed grinding and polishing. The polishing element is gimbal mounted on its lower extreme in a spherical bearing to allow a lens blank holder to follow the contour of the lens during the polishing process. The movement between the rotary drive and linear drive mechanisms independent of each other provides a balanced and low vibration operation. No specific speeds of rotation are recited and the abrasion is provided by a slurry.
U.S. Pat. No. 4,612,733 (Lee) describes a very high speed lap with a positive lift effect. The apparatus and method comprises a rotary lapping system which uses a liquid slurry of abrasive particles. The diameters of the particles are shown to be from about 1.5 to 5 micrometers, but may be outside this range. The system is described as producing positive lift by presenting leading edge surfaces with a positive angle of attack in the liquid abrasive slurry, the leading edge surfaces generating a positive lift through hydrodynamic interaction with the slurry. Each of the positive lift tools presents a grinding surface to said workpiece when it is rotated in the slurry. There is again no specific rotational speed provided in the description, and the use of liquid slurries would cause higher lapping/abrasive areas on the exterior of the grinding/lapping face as the slurry would be at higher levels at the outside of the rotating grinding area work surface.
U.S. Pat. No. 4,709,508 (Junker) describes a method and apparatus for high speed profile grinding of rotatably clamped rotation symmetrical workpieces. Rather than the grinding element contacting the surface to be ground with a grinding surface which is rotating within a plane, the edge of the grinding element (e.g., at the circumference of a disk rather than on its face) is brought against the surface to be ground.
U.S. Pat. No. 5,197,228 describes methods and apparatus for grinding metal parts, especially with devices having a cooperative workpiece holder and a tool holder which form a grinding station. The grinder table is reciprocally moveable along an axis which is at right angle to the axis of travel of the workpiece. The grinder table may also be equipped for controlled simultaneous movement along two axes. A microprocessor is designed to send and receive signals to or from all of the moving parts of the grinding machine for moving the workpiece table towards or away from the grinding bit.
U.S. Pat. No. 4,194,324 describes a carrier for semiconductive wafers during polishing steps in their manufacture. An annular flange is present to receive pressure loading from the polishing machine during the wafer polishing operation. The holder of the polishing machine includes the ability to apply a vacuum to the carrier to maintain the carrier selectively on the polishing machine. The arrangement on the equipment allows release of the vacuum during polishing and enables simple intentional removal of the carrier. Cam follower-slot arrangements permit tilting of the mounting head.
U.S. Pat. No. 5,576,754 describes a sheet holding device for an arcuate surface with vacuum retention. The sheet and device are described as useful for internal drum plotters in imaging equipment. Vacuum pressure is applied to imaging film to keep it securely positioned within the arcuate focal plane of the imaging equipment.
U.S. Pat. No. 5,563,683 describes a substrate holder for vacuum mounting a substrate. The holder is provided with two kinds of grooves or clearances in the supporting surface. Circular support faces with multiple grooves and/or a plurality of pins to support the work are shown. The device is generally described to be useful as a holder, with such particular uses as in the manufacture of semiconductors and the support of photosensitive substrate being shown. Similarly, U.S. Pat. No. 4,943,148 describes a silicon wafer holder with at least one access port providing access to the underside of the wafer with vacuum pressure. U.S. Pat. No. 4,707,012 also describes a method of applying vacuum holding forces to a semiconductor wafer during manufacture in an improved manner. U.S. Pat. No. 4,620,738 shows the use of a vacuum pickup system for semiconductor wafers. The wafers are placed into or removed from holders by the vacuum pickup.
Similarly, U.S. Pat. No. 5,414,491 describes a vacuum holder for sheet materials comprising a plurality of arrays of vacuum channels including a plurality of vacuum plenums. Flow sensors are provided so that the system can indicate the presence and/or size of the sheets being held. Specifically described are common types of imaging materials using sheets of plain paper, photographic paper and photographic film.
U.S. Pat. No. 5,374,021 describes a vacuum holding system which is particularly useful as a vacuum table for holding articles. The holding table is particularly described with respect to the manufacture of printed circuit boards. Controlled passageways are provided which are supposed to control the application of reduced pressure and to reduce the application of the vacuum when vacuum support is not required.
U.S. Pat. No. 5,324,012 describes a holding apparatus for holding an article such as a semiconductor wafer. At least a portion of the holder contacting the wafer comprises a sintered ceramic containing certain conductive materials. The use of conductive materials and fewer pores reduces the occurrence and deposition of fine particles during use. The benefits of the materials are said to be in contributions to the cleanability of the surface, insurance of mechanical strength, reduction of weight and increased dimensional stability.
U.S. Pat. No. 5,029,555 describes a holding apparatus and method for supporting wafers during a vacuum deposition process. The apparatus is an improved system for the angled exposure of at least one surface portion of a substrate supported on a surface holder to an emission of a source impinging obliquely on the surface portion. The device moves the surface holder to improve the uniformity of the emission received on the surface portion. Wheel mechanisms are coupled together to provide maintenance capability for predetermined positions of the surface. The substrate holder is moved while its orientation to the source is carefully controlled.
U.S. Pat. Nos. 4,483,703 and 4,511,387 describe vacuum holders used to shape glass. Frames are shown with slidable members moving a deformable vacuum holder between a shaping station and a mold retraction station. Pistons drive movable elements, such as the vacuum holder, on a supporting frame.
U.S. Pat. No. 4,851,749 describes a motor driven mechanical positioner capable of moving an arm to any one of about 840 discrete angular positions. An infrared light emitting device acts with a phototransistor to control the appropriate angular position. Sensing devices also act on interdependent speed controls so as to increase the accuracy of the positioning of the arm.
U.S. Pat. No. 5.180,955 describes a positioning apparatus comprising an electromechanical system which provides controlled X-Y motion with high acceleration, high maximum speeds, and high accuracy, particularly for positioning an end-effector at predetermined locations. A high speed mini-positioner is provided comprising a positioning linkage having a changeable parallelogram structure and a base structure. A main benefit of the system is the fact that the bars and bearings of the positioner are symmetrical about the X-Y plane passing through the linkage height. The symmetry means that all actuator forces and all inertial reaction forces act in vectors lying in the plane of symmetry.
U.S. Pat. No. 5,547,330 describes an ergonomic three axis positioner. The positioner is intended to move an article along three mutually perpendicular axes through system of interconnected slides and slide joints. Rack and pinions are also used to independently move the slides. The device is suggested for use in the visual inspection of work, particularly in the semiconductor industry.
U.S. Pat. No. 4,219,972 describes a control apparatus for a grinding machine. A revolution speeds changing means is provided which can selectively effect changes at high speeds when grinding and changes at low speeds when dressing the article. The relationship and control of the timing of the speed changes and the operations detection circuits and timers.
U.S. Pat. No. Re. 30,601 describes an apparatus and method particularly effective in the positioning of a semiconductor wafer in a preferred plane with respect to a photomask. Sensors regularly monitor the position of the wafer and a reference plane. A photoalignment system is provided in which a wafer is not physically touched by any portion of the photoalignment tool, thereby avoiding any contamination.
These systems have been described as providing benefits to particular technical and commercial fields, but they have not been shown to provide any particular benefits to truly high speed lapping/polishing systems and materials.